Many electronic circuits, such as processors, have several different devices incorporated therein that are connected together. One device that may be incorporated into a processor is an input/output device, which is sometimes simply referred to as an I/O device. I/O devices serve to input and output data to and from the processor. Many of these I/O devices have power supplies that are separate or isolated from power supplies connected to other devices incorporated into the processor. More specifically, the power supply associated with an I/O device is typically required to be isolated from the resonance of the other power supplies or anomalies may occur in the operation of the I/O device. In addition, the power supply associated with the I/O devices may operate at a different potential than other devices.
The electric circuit typically has bypass capacitors associated with the I/O device. Some bypass capacitors improve edges on digital signals, which improves the operation and speed of the I/O device. The bypass capacitors typically have resistors connected to them in order to form RC filters. Therefore, the bypass capacitors use area on the electronic circuit for both the capacitors and the resistors.
Another device typically incorporated into an electronic circuit is an electrostatic discharge device. The electrostatic discharge device serves to protect the devices, and the electric circuit as a whole, from electrostatic discharge by grounding transient voltages associated with electrostatic discharge. More specifically, current generated by a transient is discharged by the electrostatic discharge device to ground via a low resistance path. Therefore, the transient is discharged without damaging devices within the electric circuit.
A problem of isolating power supplies arises with high speed processors and other high speed electric circuits. A resistance in line between the power supply and the I/O devices serves to isolate the I/O devices from resonance caused by other devices connected to the power supply. However, the resistance counters the effectiveness of the electrostatic discharge device. Therefore, there is a tradeoff between reducing the resonance on the I/O power supply and the effectiveness of the electrostatic discharge device.
Another problem arises by the amount of space required for the resistors associated with the bypass capacitors. There are typically a large number of resistors used with the bypass capacitors, which uses space that could otherwise be used for other devices to improve the operation of the electronic circuit.